Polymeric compositions comprising highly ionic water dispersible polyester resins have been found useful in numerous industrial applications, including textile finishing, photoresists and laminating adhesives. Coatings prepared from these polymeric compositions are water sensitive. Such coatings often create problems such as blocking in high humidity and losing integrity or eventually dissolving when exposed to an aqueous environment.
Attempts to make latex compositions from hydrophobic polyesters by homogenizing processes using low-boiling, water-immiscible organic solvents have been generally unsuccessful. These methods produce large polymer particles which settle rapidly on storage.
U.S. Pat. No. 3,563,942 discloses polyester latex compositions in which the polyesters contain about 1-2 percent moles metal salt of a sulfonated aromatic compound such as dimethyl 5-sodiosulfoisophthalate. The latex compositions are prepared by dissolving the polyester in water immiscible organic solvents, and subsequently homogenizing in an aqueous medium containing a large excess of surfactant. Solvents are then removed by evaporation. However, the polymeric latex compositions produced according to this method are also susceptible to water because of high levels of surfactant. In addition the coated layers are hazy or opaque and the films lack the desired physical strength.
There is a continuing need for polymeric latex compositions from which water resistant coatings can be prepared. Such water resistant coatings would be extremely useful for coating objects exposed repeatedly to an aqueous environment.